He is an author of musicological studies and works devoted to Slovak music production and compositional and theoretical problems with emphasis on work of Ján Cikker. Selection of publications: Slovenská hudba v profiloch a rozboroch (Bratislava 1964), Situácia slovenskej hudobnej kultúry v rokoch 1939 – 1948 (In: Slovenská hudba 1968/4), Princíp riadenej aleatoriky z kompozičného a teoretického hľadiska (manuscript, 1982), Úvod do štúdia teórie harmónie (Bratislava 1960, 1972, 1984), Reflexie o duchovnej hudbe 20. storočia (In: Slovenská hudba, 1995/1), Genéza hudobného myslenia Jána Cikkera (manuscript).
“As part of his theoretical activity Hrušovský was devoted to the music of the 20th Century and particularly to the development of modern Slovak music. As a composer he was initially under the strong influence of A. Moyzes and fluctuated within an extended tonality using modal elements, favoring rich instrumentation and epic breadth (Pastorálna suite / Pastoral Suite; Tatranská poéma / Poem of the Tatras). At the same time he began to search within the sphere of the sonority, liberating the sound from subordination to the harmonic structure (mainly in his compositions for the choir). During the 1960s Hrušovský absorbed the ideas of serial techniques (in its purest form he applied it in Combinazioni Sonoriche) and controlled aleatory (Sonata for Piano), and by using these ideas, like W. Lutosławski, he focused on developing new sound and expressive possibilities (Sen o človeku / Dream About A Man; Tri madrigalové impresie / Three Madrigal Impressions). By his mature period his musical language used modal elements, specifically polymodal elements (Musica Nocturna), and Slovak folk music idioms, and he does not stand in opposition to Moyzes and his generation; instead he left behind – in the technical and aesthetic sense – their ties to late romanticism and impressionism. Hrušovský's work of the 1970s – 1990s is characterized by the synthesis of different, often historically distant compositional techniques (including elements of classical sonata form, baroque suite or madrigal), and points to the interconnection of the present and the past in the development of music, deepening his expressive concentration and suggests but is non-pathetic to philosophical statement (Canti, symphonies, spiritual songs).”
(ZVARA, Vladimír: Ivan Hrušovský. In: 100 slovenských skladateľov. Ed. Marián Jurík, Peter Zagar. Bratislava : Národné hudobné centrum, 1998, p. 125 – 126.)